My wireless network consists of a 4th generation AirPort Extreme running 7.6.1 and a second generation AirPort Express running 7.6.2 wirelessly extending my network. The AirPort Extreme is in bridge mode from a Comcast cable modem and has an attached USB 2TB hard drive used as a time machine wireless backup for 3 macs, two running 10.8.2 and one running 10.7.5. Many other devices attach from Windows 7 and XP machines to iPads and iPhones. All work well.
Using the latest client I upgrade the Airport Express to 7.6.3 then applied the upgrade to the AirPort Extreme. All devices connect as before with 2.4GHz and 5GHz connections as often and in the same places as before the upgrade. YMMV.